黄河源地区优云湖相地层环境代用指标反映的古环境变化

通过对黄河源地区优云湖相地层剖面的研究,综合分析了剖面的粒度、碳酸盐含量、磁化率、TOC、N和C/N比值环境代用指标,获得了这一地区中更新世中晚期古湖泊环境变化记录。结果显示该古湖泊465～219 kaB.P.期间可能经历了深湖-滨浅湖-深湖-浅湖-深湖5个湖泊演化过程。465～435.2 kaB.P.期间,降水量较多,入湖径流多,气候比较冷湿,为深湖环境;435.2～367.3 kaB.P.期间,入湖径流减少,湖水水动力减弱,环境温度较低,湖泊营养状态较差,有机物主要是陆源物质,为浅湖环境;367.3～284.6 kaB.P.期间,环境温度逐渐增高,湖泊的营养状态好转,湖泊水体体积逐渐增大,为深湖环境;284.6～228.2 kaB.P.期间湖泊为浅水环境,但环境温度低,湖泊的营养状态差,湖泊水体体积逐渐增加,后期向深湖转变;228.2～219.0 kaB.P.期间,环境温度低,湖泊的营养状态差,湖泊水体体积逐渐增加,为深湖环境。优云地区中更新世中晚期的环境代用指标在约370 kaB.P.和约250 kaB.P.发生突变,这两次突变分别与深海氧同位素曲线MIS11向MIS10转变时期和MIS8向MIS7转变时期相对应,反映该区及青藏高原东北部的气候环境演变特征具有全球变化特征。

Characteristics of Environmental Proxies of Lacustrine Stratum in Youyun and the Reflection of Paleoenvironmental Changes in Yellow River Source Region

The records of Mid-Pleistocene lake environmental change have been obtained by comprehensively analyzing characteristics of environmental proxies of lacustrine section in Youyun in Yellow River source region,such as granularity,carbonate content(C),magnetic susceptibility,TOC,nitrogen content(N) and C/N ratio.The results show that the paleaolake might have experienced five progresses of lake evolution from 465 kaB.P.to 219 kaB.P,i.e.deep lake,shallow lake,deep lake,shallow lake and deep lake.During the period of 465 kaB.P.to 435.2 kaB.P.,the paleaolake was in a deep lake environment with more precipitation and more runoff into the lake,and the climate is cold and wet.During the period of 435.2 kaB.P.to 367.3 kaB.P.,the paleaolake was in a shallow lake environment with the reduction of precipitation and runoff into the lake,and the hydrodynamics of the lake water was weakened;the surrounding temperature was low;the nutrition of the lake was poor and the organic matters of terrestrial origin were in majority.During the period of 367.3 kaB.P to 284.6 kaB.P.,the paleaolake was in a deep lake environment with gradually increasing temperature of surrounding;the nutritional status was improved;the volume of the lake water increased.During the period of 284.6 kaB.P.to 228.2 kaB.P.,the paleaolake was in a shallow lake environment with low temperature,and the nutrition of the lake was poor;the water volume gradually increased afterwards,and the lake changed to deep water.During the period of 228.2 kaB.P.to 219.0 kaB.P.,the paleaolake was in a deep lake environment with low temperature;the nutrition of the lake was poor;the volume of lake water was large.The environmental proxies had two sudden changes in 370 kaB.P.and 250 kaB.P.,and the two sudden changes corresponded to the change of MIS11 to MIS10 and MIS8 to MIS7 in the deep-sea oxygen isotope curve,respectively.This result reveals that the environmental evolution in northeastern Qinghai-Tibet Plateau area was in accordance with the global environmental evolution.